Zoom lens

Abstract

A zoom lens includes, sequentially from an object side, a first lens group having a positive refractive power; a second lens group having a negative refractive power; a third lens group having a positive refractive power; and a fourth lens group having a positive refractive power. Zoom is performed by moving the second and the third lens groups in a direction along an optical axis. The fourth lens group consists of, sequentially from the object side, a front group having a positive refractive power, an intermediate group configured by a cemented lens formed by a positive lens and a negative lens and having an overall refractive power that is negative, and a rear group having a positive refractive power. Blur is corrected by moving the intermediate group in a direction that is substantially orthogonal to the optical axis.

What is claimed is: 
     
       1. A zoom lens comprises sequentially from an object side:
 a first lens group having a positive refractive power; 
 a second lens group having a negative refractive power; 
 a third lens group having a positive refractive power; and 
 a fourth lens group having a positive refractive power, wherein 
 zoom is performed by moving the second lens group and the third lens group along an optical axis, 
 the fourth lens group consists of, sequentially from the object side, a front group having a positive refractive power, an intermediate group consisting of only a cemented lens formed by a positive lens and a negative lens or a cemented lens formed by a negative lens and a positive lens and having an overall refractive power that is negative, and a rear group having a positive refractive power, 
 blur is corrected by moving the intermediate group in a direction that is substantially orthogonal to the optical axis, and 
 a conditional expression (1)1.85<|Ft×F4M/(F4F×F4R)|<4 is satisfied, where Ft represents overall optical system focal length, at a telephoto edge, in an infinity focus state, F4F represents the focal length of the front group of the fourth lens group, F4M represents the focal length of the intermediate group of the fourth lens group, and F4R represents the focal length of the rear group of the fourth lens group. 
 
     
     
       2. The zoom lens according to  claim 1 , wherein |Ft×F4M/(F4F×F4R)| is greater than or equal to 1.9082 and less than or equal to 2.3712. 
     
     
       3. A zoom lens comprises sequentially from an object side:
 a first lens group having a positive refractive power; 
 a second lens group having a negative refractive power; 
 a third lens group having a positive refractive power; and 
 a fourth lens group having a positive refractive power, wherein 
 zoom is performed by moving the second lens group and the third lens group along an optical axis, 
 the fourth lens group consists of, sequentially from the object side, a front group having a positive refractive power, an intermediate group configured by a cemented lens formed by a positive lens and a negative lens or a cemented lens formed by a negative lens and a positive lens and having an overall refractive power that is negative, and a rear group having a positive refractive power, 
 blur is corrected by moving the intermediate group in a direction that is substantially orthogonal to the optical axis, 
 a conditional expression (1)1.85<|Ft×F4M/(F4F×F4R)|<4 is satisfied, where Ft represents overall optical system focal length, at a telephoto edge, in an infinity focus state, F4F represents the focal length of the front group of the fourth lens group, F4M represents the focal length of the intermediate group of the fourth lens group, and F4R represents the focal length of the rear group of the fourth lens group, and 
 a conditional expression (2)−2.0<AT<−1.3 is satisfied, where AT is an anti-blur coefficient of the intermediate group of the fourth lens group at the telephoto edge, AT=(1−βM)×βR, βM represents lateral magnification of the intermediate group of the fourth lens group, at the telephoto edge, and βR represents lateral magnification of the rear group of the fourth lens group at the telephoto edge. 
 
     
     
       4. The zoom lens according to  claim 3 , wherein
 at least one surface of the intermediate group of the fourth lens group is aspheric, 
 the aspheric surface, compared to a spherical surface having a paraxial radius of curvature, has a shape where a positive refractive power toward the lens periphery increases or a negative refractive power decreases, and 
 a conditional expression (3)0.1<|100×ΔS/φS|<1.0 is satisfied, where ΔS represents a deviation of the paraxial radius of curvature at a height of the effective diameter of the aspheric surface of the intermediate group and aspheric surface shape and φS represents an effective diameter of the aspheric surface of the intermediate group.